I was helping a colleague recently on an issue to do with long file system paths and the challenges and limitations of handling them in .NET. I knew there were issues but could not recall all the details.
Anyway, I just came across a wrapper class on Codeplex to assist in handling long paths.
The landing page also has a link to an interesting blog series by Kim Hamilton on the Base Class Library (BCL) team that explains in detail about this topic:
Also came across this Channel 9 video about the BCL team and also the BCL in .NET 4.